A variety of systems are now known for the installation of underground pipes, particularly for the replacement of an existing deteriorated pipe. Pneumatic impact tools that bore horizontal holes or burst existing pipelines are in widespread use. See, for example, Wentworth et al. U.S. Pat. No. 5,025,868. In one widely practiced method, a pneumatic impact boring tool is sent through the existing pipeline such that the head of the tool, which may be provided with blades that apply intense local pressure to the existing pipe, fractures or splits the existing pipe. See, for example, Streatfield et. al. U.S. Pat. Nos. 4,720,211, 4,738,565 and 4,505,302. A replacement pipe, typically made of plastic such as HDPE, is drawn along behind the boring tool. This process has proven effective commercially because it bursts the old pipe and replaces it with a new pipe at the same time. However, exhaust from the impact tool is vented into the interior of the replacement pipe, which is unacceptable for certain types of pipe installations, such as gas and water lines.
Directional drilling machines are less effective for pipe bursting, especially for hard to burst pipes like cast iron, because the steady pushing force of the drill string lacks the impact power of a pneumatic impact boring tool. Thus, in some instances, a directional borer or winch is used to pull a pneumatic impact tool through an existing pipeline in order to burst the existing pipe and pull in the replacement pipe. These alternatives are effective but require considerable equipment and manual labor.
Wentworth U.S. Pat. No. 5,782,311 describes a pipe bursting apparatus using a directional boring machine capable of simultaneously rotating and pulling a drill string and an impact tool connectable to the drill string. The impact tool includes a tubular housing ending in a front bursting head, an input shaft, bearings supporting the input shaft for rotation within the housing, a striker disposed for reciprocation within the housing to deliver impacts to a front anvil, and a drive mechanism for simultaneously pulling the impact tool forward in response to a pulling force on the input shaft and for reciprocating the striker to drive the tool forward by the action of cyclic impacts on the front anvil. The apparatus can carry out a pipe bursting operation in a manner that eliminates the need to use a separate pneumatic impact tool to burst the existing pipe. The present invention provides an impactor which operates using a pressure fluid such as compressed air, and which can be readily used with existing directional boring machines.
A number of cable operated static bursting systems have been used for pipe bursting. Carter et al. PCT Publication WO 98/30350 describes a pipe bursting system that makes use of a relatively small, light weight hydraulic cable puller to pull a pipe bursting mole. Fisk et al. U.S. Pat. Nos. 4,983,071 and 5,078,546 describe a cable-drawn tool backed by an impact tool and provided with a blade for slitting and expanding a steel gas main. Wentworth et al. U.S. Pat. No. 6,269,889 illustrates another bursting method wherein a pneumatic tool drawn by a conventional winch is used for pipe bursting. In general systems, that rely only on static pulling force either cannot handle large pipe sizes or require a very large, powerful pulling system that is expensive and labor intensive to use. System combining pulling force with an impact tool have been able to handle larger pipe sizes than comparable static force only systems, but difficulties have been encountered with starting and stopping the tool during a run. When the tool is far down the bore, it can be difficult to re-start the tool. The present invention addresses this disadvantage among others.